Yeah I think time is probably the best way to determine whether someone has hair extensions. But with Olivia Rodrigo it is harder to tell. Certainly I think she has long hair and you can even look back at photos/videos from the past and see that her hair went from a shorter length to a longer length gradually but I do think there appears to be disparities between her hair length at some public appearances and candid photos just before her recent tour began and her hair length on the current tour. It's hard to say though because different clothing types/items might maker her hair look slightly longer or shorter relatively and because of differing camera angles in pics/vids.